Molecularly imprinted polymer beads for extraction of metals and uses thereof

ABSTRACT

The present disclosure provides Molecularly Imprinted Polymer (MIP) technology for selectively sequestering one or more target molecules from chemical mixtures. Also disclosed herein are MIP beads and methods of making and using thereof.

BACKGROUND

Extraction and recovery processes are common, for example in waterpurification, mining, and waste treatment. While the specific unitoperations and process chemistries may be different for these processes,the basic approach is the same—elaborate mechanical and chemicalprocesses which are usually lengthy, energy intensive, and expensive.Many of these processes utilize, at least in part, absorbents such asactivated carbon or ion exchange absorbents to remove or sequesterdissolved species.

Carbon, particularly activated carbon, is a common absorbent, but isrelatively nonspecific. Molecularly imprinted polymers (“MIPs”) havebeen developed with substantially improved specificity for a “target”molecule which would be desirable to remove from a process stream (e.g.,in waste treatment applications) or to sequester (e.g., isolate) from aprocess stream because of its value. MIPs are polymers designed to behighly selective for a specific target molecule. MIPs are prepared bypolymerizing a polymerizable ligand which coordinates or “binds” to thetarget molecule. The target molecule and the polymerizable ligand areincorporated into a pre-polymerization mixture, allowed to form acomplex, then polymerized (typically in the presence of one or morenon-ligand monomers and a cross-linking monomer). The target moleculethus acts as a “template” to define a cavity or absorption site withinthe polymerized matrix which is specific to the target molecule (e.g.,has a shape or size corresponding to the target molecule). The targetmolecule is then removed from the MIP prior to its use as an absorbent.

However, while highly selective to the desired target molecule, MIPshave significant drawbacks. For example, if the target molecule ishighly valuable (e.g. a precious metal) or hazardous (e.g., toxic orradioactive), the need to use the target molecule itself as a templatein preparing the MIP can be prohibitively expensive due to e.g., thecost of the target molecule or the precautions required to handle thetarget molecule compared to less selective, but far cheaper absorbants.In addition, because the target molecule must remain complexed to thepolymerizable ligand during the polymer synthesis, if the targetmolecule/polymerizable ligand complex is unstable or otherwiseincompatible with the polymerization conditions (e.g., catalyst, othermonomers, low solubility, etc.) it may not be possible to prepare theMIP at all, or require complex or difficult reaction conditions.Accordingly, it would be desirable to prepare absorbents with theadvantageous selectivity and other characteristics of conventional MIPmaterials, but without the disadvantages inherent in using the targetmolecule as a template in preparing the MIP. The methods and materialsof the present disclosure provide such improvements over conventionalMIP materials and processes.

SUMMARY

The present disclosure relates generally to molecularly imprintedpolymers. More particularly, the present disclosure relates to cationicmolecularly imprinted polymer beads for binding target compoundsutilizing organic anions as surrogates for anionic metal complexes withsimilar charge and molecular structure. As such, the present disclosureinvolves the fields of chemistry, polymers, and materials science.

The present disclosure, in part, provides macroreticular polymer beadsand methods of making and using thereof. The present disclosure alsoprovides methods of selectively sequestering one or more target metalions from a solution of the one or more target metal ions admixed withother ions. This disclosure addresses the need for new MIP technologiesthat can be used to selectively isolate the desired target in goodyield, with high target removing efficiency, good capacity for thetarget, and be regenerable.

One of the embodiments of the present disclosure relates to a pluralityof macroreticular polymer beads comprising a copolymer having aplurality of complexing cavities which selectively bind a target metalion, wherein the copolymer is prepared from:

-   -   (a) a ligand monomer which is cationic or anionic and is        complexed to a non-metal surrogate ion,    -   (b) an uncharged monomer, and    -   (c) a crosslinking monomer;        -   wherein:    -   (i) the charge of the copolymer in the complexing cavity is        opposite the charge of the target metal ion, and    -   (ii) the non-metal surrogate ion has substantially the same        shape and charge as the target metal ion.

Another embodiment relates to a method of preparing macroreticularmolecularly imprinted polymer beads comprising polymerizing:

-   -   (a) a ligand monomer which is cationic or anionic and is        complexed to a non-metal surrogate ion,    -   (b) an uncharged monomer, and    -   (c) a crosslinking monomer;    -   thereby forming a plurality of macroreticular molecularly        imprinted polymer beads, each having a plurality of complexing        cavities which selectively bind a target metal ion, wherein the        size and charge of the non-metal surrogate ion is substantially        the same as the target metal ion.

Some embodiments relate to a method of selectively sequestering one ormore target metal ions from a solution of the one or more target metalion ions admixed with other ions, comprising first contacting themacroreticular polymer beads with a stripping solution, whereby thenon-metal surrogate ions are removed from the macroreticular polymerbeads, then contacting the stripped beads with the solution, therebyselectively sequestering the target ion in the macroreticular polymerbeads.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. In the case of conflict, thepresent specification, including definitions, will control. In thespecification, the singular forms also include the plural unless thecontext clearly dictates otherwise. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of the present disclosure, suitable methods andmaterials are described below. All publications, patent applications,patents, and other references mentioned herein are incorporated byreference herein, for all purposes. The references cited herein are notadmitted to be prior art to the claimed inventions. In addition, thematerials, methods, and examples are illustrative only and are notintended to be limiting.

Other features and advantages of the present disclosure will be apparentfrom the following detailed description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of the MIP production process.

FIG. 2 provides a comparison of a MIP of the present disclosure(“Protol”), compared to activated carbon (“Carbon”) in Au(CN)₂ ⁻sequestration for a simulated gold leach process stream.

FIG. 3 provides a comparison of an exemplary MIP process (“6WIC Beads”)vs. a conventional activated carbon process.

DETAILED DESCRIPTION

The present disclosure is directed, in various embodiments, to improvedmethods for preparing molecularly imprinted polymer (“MIP”) absorbentsor materials, MIP absorbents or materials prepared by such processes,and improved processes utilizing the MIP absorbents or materials of thepresent disclosure.

Absorption-based processes are often designed to separate, extract, orsequester a specific molecular specie or “target” molecule from amixture, either to isolate the target molecule (e.g., because of itsvalue), remove a specific specie from a mixture (e.g., because of itstoxicity or other hazardous properties), or to detect the targetmolecule (or molecules associated with the target molecule). Molecularlyimprinted polymers are highly selective absorbents with absorption sitesspecifically tailored to bind to a particular target molecule. Examplesof known MIPs and methods of preparing and using MIPs include thosedisclosed in U.S. Pat. Nos. 7,067,702; 7,319,038; 7,476,316; 7,678,870;8,058,208; 8,591,842, which are incorporated by reference herein intheir entirety for all purposes. These MIPs are copolymers prepared bypolymerizing a polymerizable ligand for the target molecule (i.e., a“ligand monomer”) in a polymer matrix composed of one or more non-ligandmonomers (e.g., styrene or other monomers which do not form a complexwith the target molecule), and one or more crosslinking agents.Conventionally, the “templated” absorption sites characteristic of MIPsare prepared by forming an appropriate complex of the ligand monomerwith the target molecule, then polymerizing the resulting targetmolecule-ligand monomer complex in the presence of one or morenon-ligand monomers and at least one cross-linking agent, under suitablepolymerization conditions. The resulting polymer structure comprises amatrix of the polymerized non-ligand monomer(s) with dispersed bindingsites or cavities (“complexing cavities”) containing the targetmolecule, still complexed to the (now polymerized) ligand monomer.Because the polymerization is carried out in the presence of the targetmolecule, the target molecule forms a “template” so that the size andshape of the complexing cavity is specific to the particular targetmolecule, resulting in highly selective binding to the target moleculerelative to other molecules. A schematic diagram of the templatingprocess for preparing MIP materials is shown in FIG. 1.

As discussed above, while utilizing the target molecule as a moleculartemplate provides highly selective complexing cavities optimal forbinding the target molecule, the conventional MIP manufacturing processposes significant manufacturing and/or scale-up problems due to the needto use the target molecule itself in manufacturing. Large scalemanufacturing would therefore require use of large amounts of the targetmolecule, which can be a particular problem (even in small scalemanufacturing) if the target molecule is expensive, relativelyunavailable, toxic, radioactive, interferes with the polymerization ofthe MIP, etc., or any combinations of these factors.

Surprisingly, Applicants have found that the selectivity advantages ofconventional MIPs can be retained without the need to use the targetmolecule itself as a template for the binding site, by substituting anappropriately selected “surrogate” molecule for the target molecule. Aswill be exemplified herein, a MIP selective for target molecule “A” canbe prepared by polymerizing a complex of a suitable surrogate molecule“B” with ligand monomer(s), non-ligand monomer(s) and crosslinkingmonomer(s), provided that “A” and “B” complex to the ligand monomerusing the same physicochemical mechanism, have similar size and/orshape, and “B” is one or more of less expensive, less hazardous (i.e.,toxic, radioactive), or more compatible with the polymerizationconditions compared to “A.” The resulting “surrogate” templated MIPs,while perhaps somewhat less selective for the target molecule than thoseprepared using the conventional process (in which the target moleculeserves as the molecular template) are much less expensive, safer toprepare, easier to manufacture and scale-up, etc., yet sufficientlyselective in e.g., separation or extraction applications to be similarin performance to conventional MIPs, yet substantially lower in cost.Moreover, the “surrogate” templated MIPs of the present disclosureprovide substantial improvements in overall separation process costs dueto their combination of high performance at relatively low cost.

While various exemplified embodiments of MIP materials and methodsdisclosed herein relate to ionic MIPs, any suitable physicochemicalinteraction for binding a particular target molecule can be employeddepending on the chemical structure and characteristics of the targetmolecule. Various different physicochemical interactions between theligand monomer and target molecule which can be exploited to prepareMIPs materials according to the disclosure include covalent, ionic,ion-dipole, hydrogen bonding, dipole-dipole, induced dipole orinstantaneous dipole-induced dipole (i.e., London dispersion) attractiveinteractions, and minimizing coulombic and steric repulsiveinteractions. When the target molecule is an ion (e.g., a “target ion”),it is convenient to utilize ionic interactions by selecting a ligandmonomer having an ionic functional group of complementary charge. Forexample, when the target ion is cationic, the ligand monomer includes ananionic functional group (e.g., a carboxylate, sulfonate, phosphonate,or other acid salt) capable of forming a complex with the cationictarget ion, and when the target ion is an anion, the ligand monomerincludes a cationic functional group (for example a quaternary ammoniumion) capable or complexing with the anionic target ion. When targetmolecule is neutral (i.e., has no formal charge), suitable unchargedligand monomers include but are not limited to monomers includingfunctional groups such as amines, phosphines, esters, ethers, cryptands,thio ethers, Schiff bases and the like. Neutral target moleculestypically include, for example small organic molecules such as but notlimited to pesticides, drug molecules, radiotracers, and the like.

Suitable surrogates can be selected by first characterizing the size,shape, and relevant physicochemical characteristics of the targetmolecule. Candidate surrogate molecules of similar molecular shape andsize, and similar physicochemical characteristics can then be identifiedby, for example, molecular modeling using commercially availablemolecular modeling programs such as ChemBioDraw® Ultra 14.0 For example,if the target molecule is ionic, the surrogate ion would be selected tohave a similar size, shape, and charge as the target ion.Advantageously, the surrogate should be relatively inexpensive,non-toxic, and not interfere with the polymerization (i.e., should notform a highly unstable complex with the ligand monomer, poison thepolymerization catalyst, inhibit the initiator, react with othermonomers or polymerization solvents, be insoluble in the polymerizationsolvent, etc.).

Polymerizable ligands, for instance 4-vinylbenzyl tri-n-butyl ammoniumchloride and other cationic ligands as described herein, have beendesigned for the extraction of anionic metallic salts from aqueoussolutions. Such ligands are soluble in water until reacted or complexedwith an anion, such as thiocyanate, and then precipitate from solution.The resulting precipitate is soluble in an organic solvent. The anion,such as thiocyanate, mimics the molecular shape and charge of aparticular target metal anion, such as dicyanoaurate or dicyanoargenate,both of which are linear molecules with a single negative charge. Theresulting ligand/anion pair is then polymerized into a hydrophobicpolymer matrix, such as styrene, to form porous beads or particles,which can then be utilized for the selective removal of the desiredmetal anion (e.g., dicyanoaurate or dicyanoargenate) from an aqueoussolution.

The use of a ligand/anion complex for producing ion selective MIP resinsprovides a material superior to existing ion-exchange resins, forexample with improved selectivity for target ions, maintaining betteractivity during use, reduced need for multiple process steps to separatethe target ion from other species which compete for the ion exchangebinding sites, and improved regeneration properties. The use of such“surrogates” instead of the target ion in preparing MIPs also reducesthe overall cost for developing and scaling up molecularly imprintedpolymer resins, as well as reducing the amount of potential hazardouswaste and/or reclamation of the target molecule (for further use), andtheir associated costs for processing.

MIP beads according to the present disclosure can have any suitableshape, ranging from approximately spherical, to elongated, irregular(e.g., similar to the irregular shape of cottage cheese curds), orformed to specific desired shapes.

In various embodiments, it is desirable that the molecularly imprintedpolymer be in the form of beads, particularly porous beads that havesufficient porousity so as to allow facile mass transport in and out ofthe bead.

The term “bead” refers to a plurality of particles with an averageparticle size ranging from about 250 μm to about 1.5 mm. In someembodiments, the average particle size of the beads can be about 250 μm,about 300 μm, about 350 μm, about 400 μm, about 450 μm, about 500 μm,about 550 μm, about 600 μm, about 650 μm, about 700 μm, about 750 μm,about 800 μm, about 850 μm, about 900 μm, about 950 μm, about 1000 μm,about 1050 μm, about 1100 μm, about 1150 μm, about 1200 μm, about 1250μm, about 1300 μm, about 1350 μm, about 1400 μm, about 1450 μm, or about1500 μm, including any ranges between any of these values. In particularembodiments, the average particle size range is from about 0.3 mm to 1.1mm.

In some embodiments, the MIP beads of the present disclosure have asubstantially unimodal particle size distribution. In other embodiments,it may be desirable for the MIP beads to have a bimodal or othermultimodal particle size distribution.

In many processes, material handling or mass flow requirements dictatethat the percentage of fine particles be low. Accordingly, in particularembodiments, less that about 10% of the MIP beads of the presentdisclosure have a particle size less than about 250 μm. In otherembodiments, less than about 5% or less than about 1% of the beads havea particle size less than about 250 μm. The average particle size of thebeads may be measured by various analytical methods generally known inthe art including, for example, ASTM D 1921-06.

Alternatively, the molecularly imprinted polymer can be in a non-beadform, such as nanowires, thin films or membranes, or powders. MIPsaccording to the disclosure can be used as ionophores in liquidelectrodes or as coatings for graphite electrodes to provide highlysensitive MIP ion-selective electrodes for detection of a variety ofdrugs and other chemical compounds.

In most embodiments, it is desirable that the beads of the presentdisclosure be porous to facilitate mass flow in and out of the bead. Inparticular embodiments, the MIP beads of the present disclosure arecharacterized as “macroreticular” or “macroporous,” which refers to thepresence of a network of pores having average pore diameters of greaterthan 100 nm. In various embodiments, polymer beads with average porediameters ranging from 100 nm to 2.4 μm are prepared.

In some embodiments the average pore diameters can be about 100 nm,about 200 nm, about 300 nm, about 400 nm, about 500 nm, about 600 nm,about 700 nm, about 800 nm, about 900 nm, about 1000 nm, about 1100 nm,about 1200 nm, about 1300 nm, about 1400 nm, about 1500 nm, about 1600nm, about 1700 nm, about 1800 nm, about 1900 nm, about 2000 nm, about2100 nm, about 2200 nm, about 2300 nm, or about 2400 nm, includingranges between any of these values.

The beads can also be mesoporous, or include mesopores (in addition tomacropores). The term “mesoporous” refers to porous networks having anaverage pore diameter from 10 nm to 100 nm. In some embodiments mesoporeaverage pore diameters can be about 10 nm, about 15 nm, about 20 nm,about 25 nm, about 30 nm, about 35 nm, about 40 nm, about 45 nm, about50 nm, about 55 nm, about 60 nm, about 65 nm, about 70 nm, about 75 nm,about 80 nm, about 85 nm, about 90 nm, about 95 nm, or about 100 nm,including any ranges between any of these values.

In addition, the beads can also be microporous, or include micropores inaddition to macropores and/or mesopores. The term “microporous” refersto porous networks having an average pore diameter less than 10 nm. Insome embodiments micropore average pore diameters can be about 0.5 nm,about 1 nm, about 1.5 nm, about 2 nm, about 2.5 nm, about 3 nm, about3.5 nm, about 4 nm, about 4.5 nm, or about 5 nm, or about 5.5 nm, about6 nm, about 6.5 nm, about 7 nm, about 7.5 nm, about 8 nm, about 8.5 nm,about 9 nm, about 9.5 nm, or about 10 nm, including ranges between anyof these values.

The macroreticular polymer beads have a surface area of about 0.1 toabout 500 m²/g, for example about 0.1, about 0.5, about 1, about 5,about 10, about 15, about 20, about 30, about 40, about 50, about 60,about 70, about 80, about 90, about 100, about 150, about 200, about250, about 300, about 350, about 400, about 450, or about 500 m²/g,inclusive of all ranges and subranges therebetween.

The structure and porosity of the beads are determined principally bythe conditions of polymerization. The desired porosity of the bead canbe achieved by the choice of surrogate/ligand monomer complex,non-ligand monomer and crosslinking agents and their amounts, as well asthe composition of the reaction solvent(s) and optional pore formingadditives or thixotropic agents. Porosity determines the size of thespecies, molecule or ion that may enter a specific structure and itsrate of diffusion and exchange, as well as the rate of mass flow in andout of the bead structure.

The thixotropic agents can significantly improve control of beadformation and substantially uniform bead or particle size. Suitablethixotropic agents employed herein are dependent on the type and amountof monomer employed and the suspending medium. The thixotropic agentscan also advantageously act as suspension agents during the suspensionpolymerization process. Representative examples of such thixotropicagents include, but are not limited to, cellulose ethers suchhydroxyethylcellulose, (commercially available under the trade name of“CELLOSIZE”), cross-linked polyacrylic acid such as those known underthe name of “CARBOPOL” polyvinyl alcohols such as those known under thetrade name of “RHODOVIOL”, boric acid, gums such as xanthan gum and thelike and mixtures thereof, The amount of thixotropic agents caninfluence the size of the resin (i.e., the use of larger amounts ofthixotropic agents often results in the formation of smaller resinparticles).

The amount of the thixotropic agent is generally from about 1.5 to about5 weight percent, based on the weight of the monomers in the monomermixture. In some embodiments, the amount of the thixotropic agent isfrom about 1.5 to about 2.5 weight percent, based on the weight of themonomer or monomers (combination of monomers) in the monomer mixture.

The beads of the present disclosure can be prepared by variouspolymerization techniques. A polymer matrix can then be formed via asuitable polymerization technique in the presence of thesurrogate/ligand monomer complex to form an imprinted resin. The resinproduct can be then be recovered. Non-limiting examples of suitablepolymerization techniques can include aqueous suspension polymerization,inverse suspension polymerization (e.g. in perfluorocarbon), non-aqueousdispersion polymerization, two-stage swelling polymerization, aerosolpolymerization, latex seeded emulsion polymerization,electropolymerization, and bulk polymerization on porous beadsubstrates. In one embodiment, the polymerization method is the aqueoussuspension polymerization of a copolymerizable mixture of an organicphase containing non-ligand monomer, an optional crosslinker, and thesurrogate/ligand monomer complex, and an aqueous phase containing atleast one or more thixotropic agents.

Non-covalent electropolymerized molecular imprinted polymers (E-MIPs)according to the disclosure can be used as chemosensitive ultrathinfilms with high selectivity for the detection of drugs and otherchemicals. Electropolymerization is one of the strategies for thepreparation of MIP modified electrodes. A MIP film with specialselectivity is deposited on the surface of the detector, which can beused, for example, for the analysis of proteins from biological fluidsor in pharmaceutical, agricultural, food and environmental (e.g., watertreatment) analysis.

In certain embodiments of the present disclosure, a MIP is prepared bysuspension polymerization of a surrogate/ligand monomer complex andother monomers as described herein. In the suspension polymerizationprocedure, the various phases can be thoroughly mixed separately priorto the start of the reaction and then added to the polymerizationreaction vessel. While this mixing of the ingredients can be done in avessel other than the reaction vessel, the mixing can alternatively beconducted in the polymerization reaction vessel under an inertatmosphere, particularly where the monomers being employed are subjectedto oxidation. Further, in order to improve yields and selectivity of thefinal resin product, it is desirable that the ligand monomer behydrolytically stable under polymerization conditions and in the finalproduct. For example, the ligand monomer can be hydrolytically stable ina suspension polymerization formulation and under a water treatmentenvironment such that hydrolysis is substantially avoided duringpolymerization and the useful life of the resin.

The polymerizable ligand/surrogate complex of the present disclosure canbe polymerized under suspension polymerization conditions where theaqueous phase contains thixotropic agents such as polyvinyl alcohol andboric acid in water, and the organic phase comprises, for example, thepolymerizable ligand/surrogate complex, styrene (non-ligand monomer),divinylbenzene (cross-linking monomer), organic solvents, and AIBN(initiator). The biphasic mixture is agitated, for example with astirrer. By varying the temperature, agitation, polymerizableligand/surrogate loading, solvent ratios, and degree of cross-linking,different beads structures and properties can be obtained. For example,spherical and porous beads of the desired size can be obtained bycontrolling the agitation or stirring during the polymerization. Whenthe polymerization mixture is agitated to disperse the monomersdissolved in the organic reaction medium as droplets within the aqueousphase, suitably the droplets are of such size that when transformed intopolymer beads, they are substantially spherical and porous, and of thedesired size. Unsuitable reaction conditions can lead to the formationof no or very small beads, high surrogate losses to the aqueous phase,low overall yield, and insufficient porousity such that there is poormass transfer to the complexing cavity. In a particular embodiment, theligand monomer is a polymerizable ammonium salt, such as one of thepolymerizable ammonium salts disclosed herein, and the surrogate is ananion, for example one of the anions disclosed herein. In moreparticular embodiments, the ligand monomer is a polymerizable4-vinylbenzylammonium salt and the surrogate is thiocyanate,pentathionate, isophthalate, phosphate, or succinate.

Polymerization can be carried out at any suitable temperature. In someembodiments, the reaction is carried out at an elevated temperature, forexample above about 50° C. in the presence of an optional initiator.Suitable initiators that can be used include but are not limited tobenzoyl peroxide, diacetylperoxide, and azo-bisisobutyronitrile (AIBN).The amount of initiator employed can be within the range of about 0.005to about 1.00% by weight, based on the weight of the monomer beingpolymerized. In the presence of an initiator, the temperature ofreaction is maintained above that at which the initiator becomes active.Lower temperatures, e.g. about −30′ C to about 200° C., can be employedif high energy radiation is applied to initiate polymerization. Styrenicpolymerizations can be thermally initiated.

Proper and sufficient agitation or stirring throughout thepolymerization typically provides substantially spherical and porousbeads having the desired size. For example, the polymerization mixturecan be agitated to disperse the monomers (dissolved in the solventorganic phase) in the aqueous solvent phase by shear action, therebyforming droplets. By selecting the proper level of agitation, thedroplets can be of such size that when transformed into polymer beads,they are substantially spherical and porous, and will have the desiredsize as discussed herein.

Various means are available to maintain the proper agitation. Whenpolymerization is conducted in a reactor made of stainless steel, suchreactor can be fitted with a rotatable shaft having one or more agitatorblades. When a round-bottom flask is used as a reactor, an overheadstirrer can be used to agitate the reaction medium. The amount ofagitation necessary to obtain the desired results will vary dependingupon the particular monomers being polymerized, as well as theparticular polymer bead size desired. Therefore, the agitation speedsuch as the rpm (revolutions per minute) may be regulated within certainlimits. Polymerization times can vary from about 3 hours to about 72hours, depending on the reactivity of the monomers.

When polymerization is complete, the surrogate can be removed from thetypically cross-linked polymer beads without substantially affecting thecomplexing cavity. Removal of the surrogate molecule provides e.g. abead having a porous structure with complementary molecular cavitiestherein that has high binding affinity for the target molecule (or ion).For example, when the surrogate is thiocyanate (for providing adicyanoargentate or dicyanoaurate selective cavity), the thiocyanate canbe removed (“stripped”) from the binding site in the beads by flushingwith a Fe₂(SO₄)₃ solution to provide a ligand/sulfate complex suitablefor sequestering dicyanoargentate or dicyanoaurate from e.g. a miningleach process.

In embodiments wherein the surrogate molecule is covalently bound to theligand, any appropriate method can be used to cleave the covalent bondbetween the surrogate and ligand, although the covalent bond formedshould preferably be cleaved under conditions suitable to release thesurrogate molecule after the MIP is formed, without adversely affectingthe selective binding characteristics of the MIP. To accomplish this,acetone, isopropanol, methanol or other suitable organic solvent may beused to swell the resultant polymers, allowing greater access to thecoordinated surrogate. The covalent bond can be cleaved by large changesin pH or by the addition of large amounts of a competing molecule torelease the surrogate.

The MIP materials of the present disclosure can be reused (regenerated)more than once and frequently up to about 30 times or more, depending onthe particular resin and the treated liquid medium. Regeneration can beaccomplished in much the same manner as removal of the original imprintion, e.g. stripping or washing with an appropriate solution.

Macroreticular MIP beads are particularly useful for selectivelyremoving or adsorbing target dissolved species from solutions, forexample water streams, e.g., drinking water, lakes, streams, industrialeffluent streams, mining extraction and waste streams, etc. In oneembodiment, the MIP beads of the present disclosure are prepared fromligand monomers which are ionic, for example cationic (for complexing toanions) or anionic (for complexing to cations).

In a particular embodiment, the MIP beads of the present disclosure areuseful for sequestering precious metals, such as gold (Au) or silver(Ag) from mining operations. The mining of precious metals such as goldor silver typically crushing the gold and/or silver ore, and thenextracted the crushed ore with concentrated cyanide solutions (oftenunder pressure) to form an aqueous solution containing soluble cyanidecomplexes, for example Au(CN)₂ ⁻ and Ag(CN)₂ ⁻, in addition to othercontaminants such as Hg(CN)₄ ²⁻ and inter alia various copper, nickel,zinc, cobalt, chromium, and iron salts. Alternative extraction processescan form other soluble precious metal salts such as AuCl₄ ⁻ andAu(S₂O₃)₂ ³⁻ (as well as various salts of other contaminating metalspecies). Conventionally, the soluble gold or silver complexes areextracted with activated carbon, eluted from the activated carbon, andthen electrolyzed to the metallic form.

In one of the embodiments the MIPs of the present disclosure can beuseful for detection and/or removal of rare earth metals (REMs) orelements (REEs). Due to the fact that the physico-chemical properties ofREEs are very similar, their separation from each other can be verydifficult using conventional separation methods.

REMs or REEs of the present disclosure is defined as one of a set ofseventeen chemical elements in the periodic table, specifically thefifteen lanthanides (e.g., cerium (Ce), dysprosium (Dy), erbium (Er),europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium(Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm),terbium (Tb), thulium (Tm), ytterbium (Yb) as well as scandium (Sc) andyttrium (Y).

Roughly 60% of all gold produced annually has been through somevariation of the Gold-Cyanide Process (GCP). For suitable GCP solutionsactivated carbon is the most common sequestering substrate for theremoval of dicyanoaurate, accounting for over half of all gold extracted(or over 1250 tons in 2004). Activated carbon is cheap to manufacture,absorbs gold readily, is fairly selective for gold, and has a large goldloading capacity. Unfortunately, activated carbon also has a highaffinity for mercury (II) tetracyanide and under some conditions mercury(II) tetracyanide may actually displace dicyanoaurate from the activatedcarbon. Additionally, regeneration of activated carbon is energyintensive and requires a fair amount of capital layout. Likedicyanoargentate (the silver species found in GCP), mercury (II)tetracyanide desorbs with dicyanoaurate when eluted from the activatedcarbon. Mercury (II) tetracyanide is also reduced to elemental mercuryduring the electrowinning process that isolates metallic gold.

Furthermore, the elution process is not 100% efficient for activatedcarbon and some traces of mercury remain on the activated carbon.Subsequently, upon thermal reactivation of the activated carbon, themercury is thermally reduced to mercury metal, which then volatilizesand escapes into the atmosphere. The reactivation step is unavoidable asactivated carbon also absorbs organic matter, which can foul andsubstantially reduce its capacity.

Accordingly, the recoverable capacity of activated carbon (i.e., theeffective capacity based on the amount of gold ultimately recoveredafter elution) can be quite low (as low as 1 g Au/kg C, but moretypically 3-4 g Au/kg C) due to difficulties in eluting the gold, or dueto the presence of competing contaminants in the GCP (such as organics,mercury and copper salts). This low recoverable capacity results insignificant process costs (e.g., a majority of capital costs and thebulk of the operating costs) as it requires large carbon beds, andfrequent wash cycles to recover the gold and/or silver salts.Accordingly, more efficient and selective adsorbents for gold and silverextraction processes, which elute the gold and silver salts more readilyand under milder conditions would significantly reduce the capital andoperating costs in precious metal mining (and subsequent extraction)processes. The MIP absorbents of the present disclosure provide suchimproved absorbents.

Conventional ion exchange resins have also been evaluated as moreselective and higher capacity absorbents for sequestering solubleprecious metal complexes. However, while the capacity of anion exchangeresins such as Dowex 1 and Amberlite IRA 900 RF are higher (˜5-7 g Au/kgresin, vs. ˜3-4 g Au/kg C), these resins are substantially moreexpensive compared to carbon absorbents. For example, bulk activatedcarbon costs approximately $1-2 per kg, whereas Dowex 1 or Amberlite IRA900 RF can cost from $50 to $160 per kg, respectively. Furthermore, suchanion exchange resins can only be regenerated 5-25 times, and becauselarge ion exchange beds are required to process the large fluid volumestypically encountered in gold mining leach streams, the overall capitaland operating costs of an extraction process utilizing ion exchangeresins is not markedly improved compared to conventional processes usingcarbon absorbents, as shown graphically in FIG. 2.

The MIP materials of the present disclosure, prepared using surrogatesas a template rather than the target molecule as described herein,provide superior properties compared to conventional ion exchangeresins. Conventional ion exchange materials can provide relatively highinitial loadings of the target molecule, e.g. Au(CN)₂ ⁻ and/or Ag(CN)₂⁻, but the capacity decreases rapidly in use, requiring replacementafter a relatively small number of elution cycles, and reducing theextraction capacity during use. Conventional ion exchange resins arereadily “poisoned” by the presence of other metals like copper that arenot removed during the elution cycle. In addition, conventional ionexchange resins can be sensitive to pH changes. Resin beads also swelland contract in use as the beads bind and release ions duringregeneration. Over time and under particular external conditions (e.g.,hydraulic shock, chlorine and chloramine degradation, fouling(particulate and organic), oxidation, osmotic shock from theregeneration process and basic attrition from backwash), etc. the beadscan weaken and break down. In addition, the performance of conventionalion exchange resins is highly variable depending upon the ore content ofthe gold/silver-containing solution.

In contrast, the MIP materials of the present disclosure have highselectivity for gold and silver salts (95% or higher), havesignificantly higher capacity than conventional ion exchange resins(e.g., about 20-50 g Au/kg MIP resin), better retention of capacity andless variability of adsorption during use, and lowerregeneration/elution costs. In addition, the MIP materials of thepresent disclosure are substantially less expensive to manufacture thanMIP materials using the target molecule itself to template thecomplexing cavity, and are comparable or modestly more expensive thanconventional ion exchange resins. As a result, the MIP materials of thepresent disclosure can provide substantially reduced capital and processcosts relative to conventional processes designed around conventionalabsorbents (e.g., activated carbon, conventional ion exchange resins,conventional MIP resins template with the target molecule, etc.).

Conventional MIP beads for extracting precious metals have been proposed(e.g., U.S. Pat. No. 7,746,316), as the higher selectivity for preciousmetal ions allows for smaller bed volumes of MIP beads compared toconventional ion exchange resins (or carbon), but since conventional MIPbeads are prepared using the target precious metal ions as templates forthe MIP beads, the cost of preparing the large quantities of MIP beadsrequired is prohibitive. In addition, gold and silver dicyanatecomplexes are toxic and the monomer ligand/dicyanoaurate ordicyanoargentate complexes difficult to work with in large quantities.Accordingly, there has been no practical or commercially viable way tomake MIP beads at the scales required to treat gold and silver leachstreams.

Furthermore, even though MIP beads prepared using a surrogate asdisclosed herein are theoretically less selective than those preparedusing the target ion as a template, the MIP beads of the presentdisclosure provide substantial cost savings compared to conventionalabsorbents such as activated carbon or conventional ion exchange resins.In mining operations the MIP beads of the present disclosure canincrease overall extraction by between three (3) to five (5) % and canreduce operating costs by as much as 60%. These resin beads canessentially be plug-substituted to a plant's current operations withoutplant redesign. Moreover, due to their lower manufacturing cost comparedto conventional MIP materials, the “surrogate” MIP materials of thepresent disclosure are cost effective for the extraction of lower valuemetals (e.g., copper, lithium and the like) where conventional MIPmaterials would be prohibitively expensive.

For similar reasons, treating waste water streams with MIP beads toremove toxic and/or radioactive metal complexes (e.g., Hg(CN)₄ ²⁻,UO₂(CO₃)₂ ²⁻, VO₄ ³⁻, etc.) is impractical and not commercially feasiblewith conventional MIP beads prepared using these target ions to templatethe MIP beads, again, because the scale of the respective treatmentprocesses would require correspondingly large amounts of these hazardousmetal complexes in the MIP production process.

Such scale-up problems in preparing MIP absorbents can be circumventedby replacing the respective target ion as the template in preparing theMIP with a carefully selected surrogate ion of approximately the sameshape, size and charge as the target ion, so as to create complexingcavities in the MIP similar to those which would have been created usingthe target ion itself as the template. However, the surrogates are lessexpense and more readily available than the target ion, less toxic, formsufficiently stable complexes with the ligand monomer and otherwise donot compromise the ability to polymerize the MIP. For example a suitablesurrogate for preparing molecularly imprinted polymers suitable forselectively binding Au(CN)₂ ⁻, Ag(CN)₂ ⁻ or AuCl₄ ⁻ is thiocyanate. Asuitable surrogate for preparing molecularly imprinted polymers suitablefor selectively binding Au(S₂O₃)₂ ³⁻ is pentathionate. A suitablesurrogate for preparing molecularly imprinted polymers suitable forselectively binding Hg(CN)₄ ²⁻ is isophthalate. A suitable surrogate forpreparing molecularly imprinted polymers suitable for selectivelybinding VO₄ ³⁻ is phosphate. A suitable surrogate for preparingmolecularly imprinted polymers suitable for selectively bindingUO₂(CO₃)₂ ²⁻ succinate.

In conventional processes, the goal has typically been to maximize theselectivity of the absorbent for the desired target species to beremoved or sequestered. This is particularly true for processes usingMIP materials as absorbents, as the MIP materials exhibit extremely highselectivity for the target molecule used as a template in thepreparation of the MIP material. However, the additional selectivityprovided by a MIP material prepared using the target molecule as atemplate (i.e., conventional MIP materials) does not translate into asignificant process advantage, particularly if the target molecule usedto template the MIP material is expensive, toxic, difficult to obtain,or interferes with polymerization of the MIP material itself. Suchfactors can dramatically increase the cost of manufacturing the MIPmaterial, and thereby offset any processing advantages provided by thehigher selectivity.

The present applicants have found that in many processes, it issufficient to provide a MIP material that is significantly moreselective for the desired target molecule than the other species insolution, or alternatively stated, a MIP material which is substantiallyless selective, or excludes, non-target species in the mixture to beseparated.

The MIP materials (e.g., beads or macroreticular beads) prepared usingsuitable surrogates rather than the target molecule (e.g., ion) areselective for the target molecule (e.g., ion). The selectivity of theMIP material to bind specie “A” in a mixture of “A” and specie “B” canbe characterized by a “selectivity coefficient” using the followingrelationship:

${{Selectivity}\mspace{14mu} {coefficient}\mspace{14mu} {for}\mspace{14mu} A} = \frac{\left\lbrack A^{\prime} \right\rbrack \lbrack B\rbrack}{\lbrack A\rbrack \left\lbrack B^{\prime} \right\rbrack}$

where “[A]” and “[B]” refer to the molar concentration of A and B insolution, and “[A′]” and “[B′]” refer to the concentration of complexed“A” and “B” in the MIP material.

For conventional MIP materials, prepared using the target molecule totemplate the complexing cavity, the selectivity coefficient for thetarget molecule would be higher than other species, as the complexingcavity is optimally configured for the shape, size, charge, etc. of thetarget molecule. For MIP materials prepared according to the presentdisclosure, using a surrogate molecule instead of the target molecule totemplate the MIP material, the selectivity coefficient for the surrogatemolecule would be higher than, e.g., the target molecule, but theselectivity of the MIP material for the target molecule would still besignificantly higher than for other dissolve species in the mixture tobe separated. For most separations, the selectivity coefficient for thetarget ion versus other species in the mixture to be separated should beat least about 10, at least about 11, at least about 12, at least about13, at least about 14, at least about 15, at least about 20, at leastabout 25, at least about 30, at least about 35, at least about 40, atleast about 45, at least about 50, at least about 55, at least about 60,at least about 70, at least about 80, at least about 90, at least about100, at least about 200, at least about 300, at least about 400, atleast about 500, including ranges between any of these values.

As used herein, the term “bind,” “binding,” “bond,”, “bonded,” or“bonding” refers to the physical phenomenon of chemical species beingheld together by attraction of atoms to each other through sharing, aswell as exchanging, of electrons or protons. This term includes bondtypes such as: ionic, coordinate, hydrogen bonds, covalent, polarcovalent, or coordinate covalent. Other terms used for bonds such asbanana bonds, aromatic bonds, or metallic bonds are also included withinthe meaning of this term. The selective binding interactions refer topreferential and reversible binding exhibited by the MIP for an ion(anion or cation), as described herein.

One of the embodiments of the present disclosure relates to a pluralityof macroreticular polymer beads comprising a copolymer having aplurality of complexing cavities which selectively bind a target metalion, wherein the copolymer is prepared from:

(a) a ligand monomer which is cationic or anionic and is complexed to anon-metal surrogate ion,

(b) an non-ligand monomer, and

-   -   a crosslinking monomer;

wherein:

-   -   (i) the charge of the copolymer in the complexing cavity is        opposite the charge of the target metal ion, and    -   (ii) the non-metal surrogate ion has substantially the same        shape and charge as the target metal ion.

The ligand monomers of the present disclosure include monodentate,bidentate, and polydentate ligands. The amount and type of ligandsneeded for a given cationic or anionic molecularly imprinted polymerbead would depend on the number of coordination sites available on thetarget compound and the associated ligands. Numerous combinations arepossible. For example, a target cationic ligand complex may contain atarget compound with 4 coordination sites. This target compound couldform a number of combinations with a monodentate ligand or a bidentateligand. The target compound could then bond to 1 to 4 monodentateligands or 1 to 2 bidentate ligands, assuming each ligand fullycoordinates with the target compound. Of course, the methods of thepresent disclosure contemplate partial coordination by the ligand and/ortarget compound. For example, the target ligand complex could have 1 to4 monodentate ligands or 1 to 4 bidentate ligands. Those skilled in theart can form multiple combinations of ligands and target compounds basedon the physical and chemical properties of each and the disclosureherein. In one embodiment, a mixture of ligands can be used to bind aspecific target compound.

The target cation ligand complex can be formed by a combination ofligands and target compounds that provides an overall stable complex.The methods of the present disclosure include target cationic ligandcomplexes that limit side oxidation/reduction (redox) reactions duringpolymerization. In one embodiment, the target cationic ligand complexhas a redox potential of at least 0.3 eV versus SCE (standard calomelelectrode). Additionally, the target cation ligand complex can be formedat various pH ranges. In one embodiment, the target cationic ligandcomplex can be formed in a pH range of 1 to 13. In another embodiment,the target cationic ligand complex can be polymerized in a pH range of 5to 9.

In some embodiments, the ligand molecule is a hard base ligand featuringa polymerizable group, e.g., a vinyl group.

In various embodiments, the ligand monomers of the present disclosurehave one or more cationic functional groups. Such cationic ligands canbe, but are not limited to, cationic oxygen containing heterocyclics,cationic nitrogen containing heterocyclics, cationic sulfur containingheterocyclics, cationic phosphorous containing heterocyclics, ammoniumsalts, phosphonium salts, acylinium salts, metallocenium salts,amidinium salts, imminium salts, trityl salts, pyridinium salts,pyrollidinium salts, imidizolium salts, guanidinium salts, phosphoniumsalts, sulfonium salts, or mixtures thereof. In particular embodiments,the cationic ligands are ammonium salts, such as alkyl and/orsubstituted alkyl ammonium salts. In one embodiment, the ligand can be4-vinylbenzyl-N,N-dimethyl-N-decylammonium,4-vinylbenzyl-N-decyl-N-methyl-D-glucammonium, N-methyl vinylpyridinium,or 4-vinylbenzyl-N,N-dimethyl-D-glucammonium.

The polymerizable groups of the ligand monomers can include anyconventional in the art, for example vinyl, styryl, acryloyl,methacryloyl, etc., or any of the polymerizable groups for any of themonomers disclosed herein.

In other embodiments, the ligand monomer is a 4-vinylbenzyl ammoniumcompound such as N,N,N-tripentyl-N-(4-vinylbenzyl) ammonium salts, orN,N-dimethyl-N-decyl-N-(4-vinylbenzyl) ammonium salts.

In one embodiment,N-methylvinylpyridiniumand4-vinylbenzyl-N,N-dimethyl-D-glucammonium canbe used in a reverse suspension polymerization reaction.

4-vinylbenzyl-N,N-dimethyl-N-decylammonium have shown particularly goodresults for use in removal of gold-containing cations from water (U.S.Pat. No. 7,476,316). In another embodiment,4-vinylbenzyl-N,N-dimethyl-N-decylammonium and4-vinylbenzyl-N-decyl-N-methylglucammonium can be used in a suspensionpolymerization reaction.

In some embodiments, the non-metal surrogate ion is an organic anion.Non-metal or organic surrogate ions of the present disclosure havesubstantially the same shape and charge as the target metal ions.

Substantially the same size and shape means that space filling models ofthe target molecule (e.g., a target anion) and the surrogate (e.g. anon-metal surrogate ion/organic anion) if superimposed on each othersuch that the overlap between the volumes defined by the space fillingmodels is maximized (e.g. determined by means of commercial molecularmodeling programs such as ChemBioDraw® Ultra 14.0) would differ by nomore than about 50%, for example, no more than about 50%, no more thanabout 45%, no more than about 40%, no more than about 35%, no more thanabout 30%, no more than about 25%, no more than about 20%, no more thanabout 15%, the more than about 10%, or no more than about 5%, inclusiveof all ranges and subranges therebetween.

Alternatively, a surrogate which is substantially the same size andshape as the target molecule can be functionally defined by theselectivity of the resulting MIP material for the target molecule (e.g.,target ion). Since the complexing cavity of the inventive MIP materialsis templated by a surrogate molecule rather than the target molecule,the selectivity for the MIP material for the surrogate material would behigher than for the target molecule. However, to the extent that thesize and shape of the surrogate molecule would be substantially the sameas the size and shape of the target molecule, the resulting MIP materialwould have a relatively high selectivity coefficient for the targetmolecule. Accordingly, higher selectivities for the target moleculewould be indicative that the sizes and shapes of the target andsurrogate molecules are substantially similar. In some embodiments theselectivity coefficient of the MIP materials of the present disclosurefor the target molecule, templated with a surrogate molecule, aregreater than about 10. In other embodiments, the selectivity coefficientof the MIP materials of the present disclosure are greater than: about15, about 20, about 25, about 30, about 35, about 40, about 45, about50, about 100, about 150, about 200, about 300, about 400, about 500,about 600, about 700, about 800, about 900, or about 1000, inclusive ofall ranges therebetween.

As discussed herein, the selectivity of the complexing cavity for thetarget molecule depends on the appropriate selection of a surrogatehaving substantially the same size, shape, and physicochemicalinteraction with the ligand monomer. Applicants have found that theselection of the ligand monomer can also affect the selectivity thecomplexing cavity. For example, if the target molecule is a anion (e.g.an anionic metal complex), the cationic ligand monomer can includepolymerizable ammonium salts. The selection of substituent groups on theammonium functional group can affect the ultimate selectivity of thecomplexing cavity for the target ion, as well as affect the solubilityand polymerization characteristics of the monomer ligand/surrogatecomplex. More particularly, when the target metal ion is Au(CN)₂ ⁻ orAg(CN)₂ ⁻ and the non-metal surrogate ion is thiocyanate, the ligandmonomer N,N,N-tripentyl-N-(4-vinylbenzyl) ammonium provides improved MIPproperties compared to relatively similar ligand monomers in which oneor more of the N-pentyl groups is replaced with another alkyl group.Similarly, when the target metal ion is Au(S₂O₃)₂ ³⁻ and the non-metalsurrogate ion is pentathionate, the ligand monomerN,N-dimethyl-N-decyl-N-(4-vinylbenzyl) ammonium provides improved MIPproperties compared to relatively similar ligand monomers in which withone or more of the N-methyl or the N-decyl group is replaced withanother alkyl group.

The MIP materials of the present disclosure are suitable for selectivelybinding target molecules. In particular embodiments, the targetmolecules are ionic, and the MIP materials have ligands withcomplimentary (opposite) charges, whereby the MIP material can complexwith the target ion. Suitable target ions can be any metal salt, forexample but not limited to, halides, cyanides, sulfates, chlorides,thiosulfates, carbonates, etc. of transition metals, oxyanions ofantimony, oxyanions of arsenic, oxyanions of beryllium, oxyanions ofbromine, oxyanions of carbon, oxyanions of chlorine, oxyanions ofchromium, oxyanions of nitrogen, oxyanions of phosphorous, oxyanions ofselenium, oxyanions of sulfur, oxyanions of manganese, oxyanions oftechnetium, oxyanions of boron, oxyanions of vanadium, molybdenumanions, tungsten anions, and mixtures thereof. In one embodiment, thetarget molecule can be arsenate salts, arsenite salts, nitrate salts,nitrite salts, cyanide salts, dicyanoaurate dicyanoargentate,tetrachloroaurate, Hg(CN)₄ ²⁻, VO₄ ³⁻, or UO₂(CO₃)₂ ²⁻.

A specific and non-limiting non-metal surrogate ion for Au(CN)₂ ⁻,Ag(CN)₂ ⁻, or AuCl₄ ⁻ is thiocyanate. A specific and non-limitingnon-metal surrogate ion for Au(S₂O₃)₂ ³⁻ is pentathionate. A specificand non-limiting non-metal surrogate ion for Hg(CN)₄ ²⁻ is isophthalate.A specific and non-limiting non-metal surrogate ion for VO₄ ³⁻ isphosphate. A specific and non-limiting non-metal surrogate ion forUO₂(CO₃)₂ ²⁻ is succinate.

In some of the embodiments the target metal ion is an anionic metalcomplex. The target metal ion can be selected form the group consistingof Au(CN)₂ ⁻, Ag(CN)₂ ⁻, AuCl₄ ⁻, Au(S₂O₂)₂ ³⁻, Hg(CN)₄ ²⁻, UO₂(COs)₂²⁻, VO₄ ³⁻, and combinations thereof. In some embodiments the targetmetal ion comprises a precious metal.

In some embodiments macroreticular polymer beads comprise a copolymerhaving a plurality of complexing cavities which selectively bind thetarget metal ion including Au(CN)₂ ⁻, Ag(CN)₂ ⁻, and wherein thecopolymer is prepared from a cationic ligand monomer.

In some embodiments, the target metal ion is Au(CN)₂ ⁻ or Ag(CN)₂ ⁻ andthe non-metal surrogate ion is thiocyanate.

In some embodiments, the target metal ion is Au(S₂O₃)₂ ³⁻ and thenon-metal surrogate ion is pentathionate.

Some embodiments relate to the target metal ion is Hg(CN)₄ ²⁻ and thenon-metal surrogate ion is isophthalate.

In other embodiments the target metal ion is VO₄ ³⁻ and the non-metalsurrogate ion is phosphate.

In certain embodiments the target metal ion is UO₂(CO₃)₂ ²⁻ and thenon-metal surrogate ion is succinate.

A wide variety of monomers may be used as a non-ligand monomer forsynthesizing the MIP in accordance with the present disclosure. Suitablenon-limiting examples of non-ligand monomers that can be used forpreparing a MIP of the present disclosure include methylmethacrylate,other alkyl methacrylates, alkylacrylates, allyl or aryl acrylates andmethacrylates, cyanoacrylate, styrene, substituted styrenes, methylstyrene (multisubstituted) including 1-methylstyrene; 3-methylstyrene;4-methylstyrene, etc.; vinyl esters, including vinyl acetate, vinylchloride, methyl vinyl ketone, vinylidene chloride, acrylamide,methacrylamide, acrylonitrile, methacrylonitrile, 2-acetamido acrylicacid; 2-(acetoxyacetoxy) ethyl methacrylate; 1-acetoxy-1,3-butadiene;2-acetoxy-3-butenenitrile; 4-acetoxystyrene; acrolein; acrolein diethylacetal; acrolein dimethyl acetal; acrylamide; 2-acrylamidoglycolic acid;2-acrylamido-2-methyl propane sulfonic acid; acrylic acid; acrylicanhydride; acrylonitrile; aeryloyl chloride;1-α-acryloyloxy-β,β-dimethyl-γ-butyrolactone; N-acryloxy succinimideacryloxytris(hydroxymethyl)amino-methane; N-acryloyl chloride;N-acryloyl pyrrolidinone; N-acryloyl-tris(hydroxymethyl)amino methane;2-aminoethyl methacrylate; N-(3-aminopropyl)methacrylamide; (o, m, orp)-amino-styrene; t-amyl methacrylate; 2-(1-aziridinyl)ethylmethacrylate; 4-benzyloxy-3-methoxystyrene; 2-bromoacrylic acid;4-bromo-1-butene; 3-bromo-3,3-difluoropropane; 6-bromo-1-hexene;3-bromo-2-methacrylonitrile; 2-(bromomethyl)acrylic acid;8-bromo-1-octene; 5-bromo-1-pentene; cis-1-bromo-1-propene;-bromostyrene; p-bromostyrene; bromotrifluoro ethylene;(+)-3-buten-2-ol; 1,3-butadiene; 1,3-butadiene-1,4-dicarboxylic acid3-butenal diethyl acetal; 1-butene; 3-buten-2-ol; 3-butenylchloroformate; 2-butylacrolein; t-butylacrylamide; butyl acrylate; butylmethacrylate; (o, m, p)-bromo styrene; t-butyl acrylate; 1-carvone;(S)-carvone; (−)-carvyl acetate; 3-chloroacrylic acid;2-chloroacrylonitrile; 2-chloroethyl vinyl ether;2-chloromethyl-3-trimethylsilyl-1-propene; 3-chloro-1-butene;3-chloro-2-chloromethyl-1-propene; 3-chloro-2-methyl propene;2,2-bis(4-chlorophenyl)-1,1-dichloroethylene;3-chloro-1-phenyl-1-propene; m-chlorostyrene; o-chlorostyrene;p-chlorostyrene; 1-cyanovinyl acetate;1-cyclopropyl-1-(trimethylsiloxy)ethylene; 2,3-dichloro-1-propene;2,6-dichlorostyrene; 1,3-dichloropropene; 2,4-diethyl-2,6-heptadienal;1,9-decadiene; 1-decene; 1,2-dibromoethylene;1,1-dichloro-2,2-difluoroethylene; 1,1-dichloropropene;2,6-difluorostyrene; dihydrocarveol; (±)-dihydrocarvone;(−)-dihydrocarvyl acetate; 3,3-dimethylacrylaldehyde;N,N′-dimethylacrylamide; 3,3-dimethylacrylic acid; 3,3-dimethylacryloylchloride; 2,3-dimethyl-1-butene; 3,3-dimethyl-1-butene; 2-dimethylaminoethyl methacrylate; 1-(3-butenyl)-4-vinylbenzene;2,4-dimethyl-2,6-heptadien-1-ol; 2,4-dimethyl-2,6-heptadienal;2,5-dimethyl-1,5-hexadiene; 2,4-dimethyl-1,3-pentadiene;2,2-dimethyl-4-pentenal; 2,4-dimethylstyrene; 2,5-dimethylstyrene;3,4-dimethylstryene; 1-dodecene; 3,4-epoxy-1-butene; 2-ethyl acrolein;ethyl acrylate; 2-ethyl-1-butene; (±)-2-ethylhexyl acrylate;(±)-2-ethylhexyl methacrylate; 2-ethyl-2-(hydroxymethyl)-1,3-propanedioltriacrylate; 2-ethyl-2-(hydroxymethyl)-1,3-propanediol trimethacrylate;ethyl methacrylate; ethyl vinyl ether; ethyl vinyl ketone; ethyl vinylsulfone; (1-ethylvinyl)tributyl tin; m-fluorostyrene; o-fluorostyrene;p-fluorostyrene; glycol methacrylate (hydroxyethyl methacrylate); GAGMA; 1,6-heptadiene; 1,6-heptadienoic acid; 1,6-heptadien-4-ol;1-heptene; 1-hexen-3-ol; 1-hexene; hexafluoropropene; 1,6-hexanedioldiacrylate; 1-hexadecene; 1,5-hexadien-3,4-diol; 1,4-hexadiene;1,5-hexadien-3-ol; 1,3,5-hexatriene; 5-hexen-1,2-diol; 5-hexen-1-ol;hydroxypropyl acrylate; 3-hydroxy-3,7,11-trimethyl-1,6,10-dodecatriene;isoamyl methacrylate; isobutyl methacrylate; isoprene;2-isopropenylaniline; isopropenyl chloroformate; 4,4′-isopropylidenedimethacrylate; 3-isopropyl-a-a-dimethylbenzene isocyanate; isopulegol;itaconic acid; itaconalyl chloride; (±)-linalool; linalyl acetate;p-mentha-1,8-diene; p-mentha-6,8-dien-2-ol; methyleneamino acetonitrile;methacrolein; [3-(methacryloylamino)-propyl]trimethylammonium chloride;methacrylamide; methacrylic acid; methacrylic anhydride;methacrylonitrile; methacryloyl chloride; 2-(methacryloyloxy)ethylacetoacetate; (3-meth-acryloxypropyl)trimethoxy silane;2-(methacryloxy)ethyl trimethylammonium methylsulfate; 2-methoxy propene(isopropenyl methyl ether); methyl-2-(bromomethyl)acrylate;5-methyl-5-hexen-2-one; methyl methacrylate; N,N′ methylenebisacrylamide; 2-methylene glutaronitrite; 2-methylene-1,3-propanediol;3-methyl-1,2-butadiene; 2-methyl-1-butene; 3-methyl-1-butene;3-methyl-1-buten-1-ol; 2-methyl-1-buten-3-yne; 2-methyl-1,5-heptadiene;2-methyl-1-heptene; 2-methyl-1-hexene; 3-methyl-1,3-pentadiene;2-methyl-1,4-pentadiene; (±)-3-methyl-1-pentene; (±)-4-methyl-1-pentene;(±)-3-methyl-1-penten-3-ol; 2-methyl-1-pentene; methyl vinyl ether;methyl-2-vinyloxirane; methyl vinyl sulfone; 4-methyl-5-vinylthiazole;myrcene; t-nitrostyrene; 3-nitrostyrene; 1-nonadecene; 1,8-nonadiene;1-octadecene; 1, 7-octadiene; 7-25ctane-1,2-diol; 1-octene;1-octen-3-ol; 1-pentadecene; 1-pentene; 1-penten-3-ol; t-2,4-pentenoicacid; 1,3-pentadiene; 1,4-pentadiene; 1,4-pentadien-3-ol; 4-penten-1-ol;4-penten-2-ol; 4-phenyl-1-butene; phenyl vinyl sulfide; phenyl vinylsulfonate; 2-propene-1-sulfonic acid sodium salt; phenyl vinylsulfoxide; 1-phenyl-1-(trimethylsiloxy)ethylene; propene; safrole;styrene (vinyl benzene); 4-styrene sulfonic acid sodium salt; styrenesulfonyl chloride; 3-sulfopropyl acrylate potassium salt; 3-sulfopropylmethacrylate sodium salt; tetrachloroethylene; tetracyanoethylene; trans3-chloroacrylic acid; 2-trifluoromethyl propene;2-(trifluoromethyl)propenoic acid; 2,4,4′-trimethyl-1-pentene; 3,5-bis(trifluoromethyl)styrene; 2,3-bis(trimethylsiloxy)-1,3-butadiene;1-undecene; vinyl acetate; vinyl acetic acid; 4-vinyl anisole; 9-vinylanthracene; vinyl behenate; vinyl benzoate; vinyl benzyl acetate; vinylbenzyl alcohol; 3-vinyl benzyl chloride; 3-(vinylbenzyl)-2-chloroethylsulfone; 4-(vinyl benzyl)-2-chloroethyl sulfone;N-(p-vinylbenzyl)-N,N′-dimethyl amine; 4-vinyl biphenyl(4-phenylstyrene); vinyl bromide; 2-vinyl butane; vinyl butyl ether;9-vinyl carbazole; vinyl carbinol; vinyl cetyl ether; vinylchloroacetate; vinyl hloroformate; vinyl crotanoate; vinylperoxcyclohexane; 4-vinyl-1-cyclohexene; 4-vinylcyclohexene dioxide;vinyl cyclopentene; vinyl dimethylchlorosilane; vinyldimethylethoxysilane; vinyl diphenylphosphine; vinyl 2-ethyl hexanoate;vinyl 2-ethylhexyl ether; vinyl ether ketone; vinyl ethylene; vinylethylene iron tricarbonyl; vinyl ferrocene; vinyl formate; vinylhexadecyl ether; vinylidene fluoride; 1-vinylquinoline; vinyl iodide;vinyllaurate; vinyl magnesium bromide; vinyl mesitylene; vinyl 2-methoxyethyl ether; vinyl methyl dichlorosilane; vinyl methyl ether; vinylmethyl ketone; 2-vinyl naphthalene; 5-vinyl-2-norbomene; vinylpelargonate; vinyl phenyl acetate; vinyl phosphonic acid,bis(2-chloroethyl)ester; vinyl propionate; 4-vinyl pyridine; 2-vinylpyridine; 1-vinyl-2-pyrrolidinone; 2-vinylquinoline; 1-vinyl silatrane;vinyl sulfone; vinyl sulfonic acid sodium salt; a-vinyl toluene; p-vinyltoluene; vinyl triacetoxysilane; vinyl tributyl tin; vinyl trichloride;vinyl trichlorosilane; vinyl trichlorosilane (trichlorovinylsilane);vinyl triethoxysilane; vinyl triethylsilane; vinyl trifluoroacetate;vinyl trimethoxy silane; vinyl trimethyl nonylether; vinyl trimethylsilane; vinyl triphenyphosphonium bromide (triphenyl vinyl phosphoniumbromide); vinyl tris-(2-methoxyethoxy) silane; vinyl 2-valerate and thelike.

Acrylate-terminated or otherwise unsaturated urethanes, carbonates, andepoxies can also be used in the MIP. An example of an unsaturatedcarbonate is allyl diglycol carbonate. Unsaturated epoxies include, butare not limited to, glycidyl acrylate, glycidyl methacrylate, allylglycidyl ether, and 1,2-epoxy-3-allyl propane.

Cross-linking (also crosslinking) agents or cross-linking monomers thatimpart rigidity or structural integrity to the MIP are known to thoseskilled in the art, and include di-, tri- and tetrafunctional acrylatesor methacrylates, divinylbenzene (DVB), alkylene glycol and polyalkyleneglycol diacrylates and methacrylates, including ethylene glycoldimethacrylate (EGDMA) and ethylene glycol diacrylate, vinyl or allylacrylates or methacrylates, divinylbenzene, diallyldiglycol dicarbonate,diallyl maleate, diallyl fumarate, diallyl itaconate, vinyl esters suchas divinyl oxalate, divinyl malonate, diallyl succinate, triallylisocyanurate, the dimethacrylates or diacrylates of bis-phenol A orethoxylated bis-phenol A, methylene or polymethylene bisacrylamide or26ismuth-acrylamide, including hexamethylene bisacrylamide lanthanide orhexamethylene bismethacrylamide, di(alkene) tertiary amines, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, divinyl ether,divinyl sulfone, diallyl phthalate, triallyl melamine, 2-isocyanatoethylmethacrylate, 2-isocyanatoethylacrylate, 3-isocyanatopropylacrylate,1-methyl-2-isocyanatoethyl methacrylate, 1,1-dimethyl-2-isocyanaotoethyl acrylate, tetraethylene glycol diacrylate,tetraethylene glycol dimethacrylate, triethylene glycol diacrylate,triethylene glycol dimethacrylate, hexanediol dimethacrylate, hexanedioldiacrylate, divinyl benzene; 1,3-divinyltetramethyl disiloxane;8,13-divinyl-3,7,12,17-tetramethyl-21H,23H-porphine;8,13-divinyl-3,7,12, 17-tetramethyl-21H,23H-propionic acid;8,13-divinyl-3,7,12,17-tetramethyl-21H,23H-propionic acid disodium salt;3,9-divinyl-2,4,8,10-tetraoraspiro[5,5]undecane; divinyl tin dichlorideand the like.

The MIP must have sufficient rigidity so that the target ion may beeasily removed without affecting the integrity of the polymer. In suchcases where the polymer matrix is insufficiently rigid, crosslinking orother hardening agents can be introduced. In imprinted MIP, thecross-linker (cross-linking agent or monomer) fulfills three majorfunctions: 1) the cross-linker is important in controlling themorphology of the polymer matrix, whether it is gel-type, macroporous ora microgel powder; 2) it serves to stabilize the imprinted binding site(complexing cavity); and 3) it imparts mechanical stability to thepolymer matrix. In particular embodiments, high cross-link ratios aregenerally desired in order to provide permanently porous materials withadequate mechanical stability.

Any suitable conditions effective to polymerize the monomers of thepresent disclosure to produce an MIP without dissociating theligand/surrogate complex may be used. The monomers of the presentdisclosure may be polymerized by free radical polymerization, and thelike. Any UV or thermal free radical initiator known to those skilled inthe art can be used in the preferred free radical polymerization.Examples of UV and thermal initiators include benzoyl peroxide, acetylperoxide, lauryl peroxide, azobisisobutyronitrile (AIBN), t-butylperacetate, cumyl peroxide, t-butyl peroxide; t-butyl hydroperoxide,bis(isopropyl) peroxy-dicarbonate, benzoin methyl ether,2,2′-azobis(2,4-dimethyl-valeronitrile), tertiary butyl peroctoate,phthalic peroxide, diethoxyacetophenone, t-butyl peroxypivalate,diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone,2,2-dimethoxy-2-phenylacetophenone, and phenothiazine,diisopropylxanthogen disulfide, 2,2′-azobis-(2-amidinopropane);2,2′-azobisisobutyronitrile-; 4,4′-azobis-(4-cyanovaleric acid);1,1′-azobis-(cyclohexanecarbonitrile)-; 2,2′-azobis-(2,4-dimethylvaleronitrile); and the like and mixtures thereof.

The choice of monomer and cross-linking agent will be dictated by thechemical (hydrophilicity, chemical stability, degree of cross-linking,ability to graft to other surfaces, interactions with other molecules,etc.) and physical (porosity, morphology, mechanical stability, etc.)properties desired for the polymer. The amounts of ligandmonomer/surrogate complex, monomer and crosslinking agents should bechosen to provide a crosslinked polymer exhibiting the desiredstructural integrity, porosity and hydrophilicity. The amounts can varybroadly, depending on the specific nature/reactivities of theligand/surrogate complex, monomer and crosslinking agent chosen as wellas the specific application and environment in which the polymer willultimately be employed. The relative amounts of each reactant can bevaried to achieve desired concentrations of ligand/surrogate complexesin the polymer support structure. Typically, the amount of ligandsurrogate complex will be on the order of about 0.01 mmol to about 100mmol percent of monomer, including: about 0.02, 0.05, 0.1, 0.2, 0.3,0.5, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, or 100 mmole percent of monomer. The amount ofcross-linker is typically on the order of about 1.0 to about 10 mmolepercent, including about 1.5, 2, 3, 4, 5, 6, 7, 8, or 9 mmole percent ofmonomer. The amount of a free radical initiator can be about 0.005 to 1mole percent, including about 0.01, 0.05, 0.1, 0.5, 0.6, 0.7, 0.8, or0.9 mole percent of monomer. (Molar percentages refer to the percentagerelative to the total amount of monomers prior to polymerization.)

The solvent, temperature, and means of polymerization can be varied inorder to obtain polymeric materials of optimal physical or chemicalfeatures, for example, porosity, stability, and hydrophilicity. Thesolvent will also be chosen based on its ability to solubilize all thevarious components of the reaction mixture, and form a desirable polymermorphology.

The degree of crosslinking can range from about 1% to about 95%. In someembodiments, the degree of crosslinking is from about 5% to about 80%.

Any solvent which provides suitable solubility and is compatible withthe desired reaction to the conditions to form the MIP materials of thepresent disclosure may be used. In some embodiments in which the MIPmaterial is prepared by suspension polymerization conditions, thesolvent can be a mixture of organic solvents. For example, the solventcan include long chain aliphatic alcohols such as pentanols, hexanols,heptanols, octanols, nonanols, decanols, undecanols, dodecanols,including saturated and unsaturated isomers thereof (e.g., methyl andethyl pentanols, methyl and ethyl hexanols, methyl and ethyl,hepatanols, etc.), aliphatic hydrocarbons (e.g., butanes, pentanes,hexanes, heptanes, etc.), aromatic hydrocarbons (e.g., benzene, toluene,xylenes, etc.), and combinations thereof.

The resin thus obtained is in the form of porous beads. Porous beads canhave an open cell structure such that the majority of open volumeswithin the bead are interconnected with one another and externalopenings on surfaces of the bead.

In one embodiment, the present disclosure provides a method ofselectively sequestering one or more target metal ions from a solutionof the one or more target metal ion ions admixed with other ions,comprising first contacting the macroreticular polymer beads of thepresent disclosure with a stripping solution, whereby the non-metalsurrogate ions are removed from the macroreticular polymer beads, thencontacting the stripped beads with the solution, thereby selectivelysequestering the target ion in the macroreticular polymer beads. Thesequestered target ion is then stripped from the beads with an ionicsolution capable of displacing the target ion, thereby regenerating thebeads for reuse in sequestering target ions.

In one embodiment, the target ion is dicyanoaurate (or dicyanoargentate)for example in a complex mixture obtained from the cyanide leech streamof a precious metal (e.g. gold or silver) mining operation, and the MIPmaterial of the present disclosure is a macroreticular MIP bead preparedby polymerizing styrene, divinyl benzene, andN,N,N-tripentyl-N-(4-vinylbenzyl) ammonium thiocyanate. The beads areinitially in the form of a thiocyanate salt. Before initial use, thethiocyanate anion is stripped out of the beads by contacting the beadswith a solution of Fe₂(SO₄)₃, thereby providing beads in the “sulfate”form. These beads are then contacted with a cyanide leach solutioncontaining the dicyanoaurate (or dicyanoargentate) ions (typically alsoincluding various Hg, Cu, Ni, Zn, and Fe ions). The dicyanoaurate (ordicyanoargentate) ions selectively bind to the beads. Upon reaching (ornearing) capacity, the beads are then stripped (e.g., with thiocyanatesolution) to release gold, silver, and other trace metals, and thenregenerated (e.g., using a solution of Fe₂(SO₄)₃) to for further use insequestration. Unlike conventional gold sequestration processes usingactivated carbon, such a process is simpler as it eliminates the carbonreprocessing required for a conventional process, and the stripping(elution) step can be carried out under less rigorous conditions (e.g.,lower temperature and pressure). See FIG. 3. This reduces both capitaland operating costs for the overall process relative to the conventionalactivated carbon absorbent process.

Another embodiment of the present disclosure relates to sequesteringtetrachloroaurate when chloride is used as a lixiviant for mining goldfrom refractory ores. The advantage of using chloride as a lixiviant isthat it avoids the use of highly toxic cyanide solutions, and thesubsequent disposal thereof. However, tetrachloroaurate (or oxychloridesthereof formed by hydrolysis when insufficient chloride is present) arenotoriously difficult to elute from ion exchange resins, with longelution times and only modest amounts of gold recovered. Additionally,the most commonly used eluent, thiourea, is a suspected carcinogen, andis not desirable for large-scale use. Accordingly, this process hasnumber of challenges for its widespread use in gold mining.Environmental factors, gold uptake efficiency, tetrachloroauratesorption onto a substrate, and finally efficient elution of the goldfrom the substrate are all problematic issues for chloride. While thefirst three factors remain to be addressed, it is believed that an ionicMIP bead of the present disclosure, coupled with a new elutionmethodology may quickly and efficiently elute gold as its cyanide orthiocyanate form.

Tetrachloroaurate may be rapidly reduced from Au³⁺ to Au⁺ with a mildreducing agent, such as ascorbic acid or sulfite, which are capable ofreducing Au³⁺ to Au⁺ and are relatively inexpensive, non-toxic, orotherwise compatible with the materials and process chemicals used inprecious metal extraction processes. When the reduction of the gold bythe reducing agent is performed in the presence of potassium cyanide,the resulting dicyanoaurate may be recaptured immediately, e.g., using aMIP material of the present disclosure, without loss of dicyanoaurateduring reduction. The dicyanoaurate can then be eluted with thiocyanate,a proven and very fast system. Because of the highly selective nature ofsome ion-exchange resins other metals would not be reduced alongside ofthe gold and be subsequently eluted during the thiocyanate elutionprocess.

The present disclosure provides methods for preparation of MIPs. MIPscan be prepared by modification of known techniques including but notlimited to those described in U.S. Pat. Nos. 4,406,792, 4,415,655,4,532,232, 4,935,365, 4,960, 762, 5,015,576, 5,110,883, 5,208,155,5,310,648, 5,321,102, 30 5,372,719, 5,786,428, 6,063,637, and 6,593,142,the entire contents of each of which are incorporated herein byreference in their entireties for all purposes.

The MIP materials of the present disclosure, particularly those preparedusing thiocyanate as a surrogate for dicyanoaurate or dicyanoargentate,and N,N,N-tripentyl-N-(4-vinylbenzyl) ammonium as the polymerizableligand are also particularly useful in sequestering dicyanoaurate ordicyanoargentate where the leach contains large amounts of dissolvedsolids, carbonaceous materials or significant amounts of mercury. Thepresence of carbonaceous materials in the leach is a particular problemfor conventional sequestration processes relying on activated carbon asan absorbent, as the presence of carbonaceous materials significantlylowers the capacity of the activated carbon for dicyanoaurate.Similarly, mercury in the leach stream can reduce the capacity ofconventional activated carbon or ion exchange absorbents by competingwith dicyanoaurate for absorption sites in the absorbent. In contrast,the MIP materials of the present disclosure provide superior selectivityfor dicyanoaurate, and are substantially less affected (or unaffected)by the presence of such contaminants.

With some modification, the methods of the present disclosure forpreparing e.g., dicyanoaurate selective MIP beads using a surrogate suchas thiocyanate would be applicable for sequestration of other gold saltsor for a number of other metal salts such as salts of copper, manganese,nickel, mercury, lead, uranium, cobalt, chromium, REMs, and REEs (orcombinations thereof) to name a few of the more toxic or valuedelements.

Fast and cost-effective surrogate-based molecularly imprinted polymertechniques of the present disclosure can also be applied in many areasof chemistry, biology and engineering, for example, as an affinitymaterial for sensors detection of chemical, antimicrobial, and dyeresidues in food, adsorbents for solid phase extraction, binding assays,artificial antibodies, chromatographic stationary phase, catalysis, drugdevelopment and screening, byproduct removal in chemical reactions,detection and/or sequestration of explosive(s) and explosive(s)residues, etc. Surrogate-based molecular imprinted polymers pose a widerange of capabilities in extraction through specific micro-cavitybinding sites. This technique can be also useful in selective extractionand separation of single elements from a chemical mixture.

The macroreticular beads of the present disclosure prepared using MIPtechnology are also useful in removing contaminants from an aqueousmedium, e.g., drinking water, lakes, streams, irrigation runoff,industrial effluent, mine waste, etc.

Throughout the description, where methods or processes are described ashaving, including, or comprising specific process steps, the processesalso consist essentially of, or consist of, the recited processingsteps. Further, it should be understood that the order of steps or orderfor performing certain actions is immaterial so long as the methodremains operable. Moreover, two or more steps or actions can beconducted simultaneously.

EXAMPLES Example 1 Preparation of Macroreticular Beads ExemplarySynthesis of Ligands Exemplary Synthesis of Bis(N-(4-vinylbenzyl)-N-decyl-N,N-dimethylammonium) pentathionate

N-(4-vinylbenzyl)-N-decyl-N,N-dimethylammonium chloride (1.08 g, 3.2mmol) was dissolved in deionized (DI) water (3 mL) in a 20 mL vialequipped with a micro stir bar. Sodium thiosulfate (1 g, 4 mmol) wasalso dissolved in DI water (0.67 mL) and was added the ligand solution.Immediately, the solution became thick and viscous and additional DIwater (3 mL) was added to thin the solution. The solution was cooled to0° C. with an ice bath while stirring. Concentrated hydrochloric acid(0.67 mL) was added dropwise over the course of one minute. A whitematerial quickly formed, which was then replaced by yellow oil, whichseparated from solution. The mixture was allowed to settle for overnightat 4° C. The following day the aqueous phase was decanted, and theresidue washed with water (5 ml). The residue was vacuum dried to giveoil that became waxy below 0° C., (1.30 g, 94% yield). The product wasstable for storage at 4° C. for several weeks without noticeabledegradation. NMR (400 MHz, CDCl3, Estimated 7.54-7.36 (dd, 8H);6.68-6.60 (dd, 2H); 5.78-5.73 (d, 2H); 5.31-5.28 (d, 2H); 4.78 (s, 4H);3.30-3.28 (t, 4H); 3.15 (s, 12H); 1.70 (bs, 4H); 1.25-1.19 (m, 28H);0.84 (t, 6H).

Exemplary Synthesis of N-(4-vinylbenzyl)-N,N,N-tri-n-pentylammoniumthiocyanate

A round bottom flask equipped with side arm is degassed, heated to 80°C. and maintained under inert atmosphere. 10 mL of acetonitrile isadded, and then 4-vinylbenzylchloride and tri-n-pentyl amine (dried with3 Å molecular sieves) (11.37 g, 50 mmol, TCI America) is added and keptunder inert atmosphere. The mixture is allowed to react six (6) hours at80° C. The acetonitrile is removed under vacuum and the residue is takenup in 25 mL diethyl ether. The product(N-(4-vinylbenzyl)-N,N,N-tri-n-pentylammonium chloride) is a whitesolid. The product is washed twice with 25 mL diethyl ether by addingdiethyl ether to the product and filtering using 5.5 cm Medium FastQualitative filter. The product is a white fluffy solid, which is dried3 hours under vacuum.

N-(4-vinylbenzyl)-N,N,N-tri-n-pentylammonium chloride (7.60 g, 20 mmol)is taken up in water (50 mL). Potassium thiocyanate (1.94 g, 20 mmol) inwater (30 mL) is add to the ligand solution at a rate of 5 mL/min. Awhite precipitate forms and an oil settles from the solution. The oil isrefrigerated overnight. The aqueous solution is decanted and the residuewashed with 50 mL of water. The residue is vacuum dried to give an oil(N-(4-vinylbenzyl)-N,N,N-tri-n-pentylammonium thiocyanate) that becomesglassy below 0° C., (Quantitative yield: 8.05 g).

Exemplary Suspension Polymerization Preparation of Aqueous Phase

Polyvinyl alcohol (PVOH, average Mw 89,000-98,000, 99+% hydrolyzed,10.26 g) is dissolved in water (540 mL) through gentle heating to 80° C.4.42 g of boric acid is dissolved in 135 mL in water and slowly addedwhen the PVOH cools to 50° C.

Preparation of the Organic Phase and Polymerization

5 g of the complex is combined with 48.75 mL of ethylhexanol and 1.25 mLof xylenes in a 100 mL Erlenmeyer flask equipped with a stir bar andallowed to stir until fully dissolved. 35.88 mL of styrene and 13.68 mLof divinylbenzene are combined with the solution of complex, and allowedto stir, covered with a septum, under ambient conditions. 0.5 g of AIBNis added to the solution and dissolved completely. When dissolved, thesolution is added to an addition funnel and degassed until the reactiontemperature reaches 75° C. When the temperature reaches 80° C. to thesolution is added to the aqueous phase at a rate of 1 mL/s. The reactionis allowed to proceed, with continuous agitation for approximately 8hours.

Post-Reaction Bead Cleanup

Upon completion of the reaction, the beads are recovered from theaqueous by filtration. The beads are then soaked in deionized water (200mL) for 10 minutes then filtered. Soaking in deionized water andfiltration is repeated two times. The beads are washed twice inmethanol, and twice in acetone. If desired, the beads can befractionated by size using the appropriate mesh sieves. The beads canthen be stored in water indefinitely at a temperature of 5 to 50° C.,prior to activation.

Bead Activation

Wet beads are placed into a large jacketed glass column, and allentrained air is removed. The column is then heated to 50° C. and asolution of ferric sulfate hydrate (0.22 M) is added at a rate of 0.1bed volumes/min for 15 bed volumes. The beads are then rinsed with water(10 bed volumes) at ambient to 50° C.

Properties of Macroreticular Beads Vs Activated Carbon

Macroreticular beads prepared as above were tested with a test solutionhaving the metal ion composition shown below in Table 1.

TABLE 1 Concentration of major metals and relative percentages found insynthetic flot-con pregnant solution. Metals Au Ag Cu Fe Zn HgConcentration (ppm) 21.67 27.34 476.4 3.49 237.7 4.19 Relative % 2.813.55 61.81 0.45 30.84 0.54

The beads prepared as described above were found to have a recoverablecapacity for dicyanoaurate (i.e., based on the amount stripped from thebeads after absorption) of 18 mg Auig beads, while the recoverablecapacity for gold of activated carbon was 3 mg Au/g carbon. Theselectivity of the beads for gold was 95% versus 21% for activatedcarbon. The elution time for the beads was substantially shorter thanfor activated carbon (2 hours for the beads versus 22 hours foractivated carbon), and was carried out at a much lower temperature (roomtemperature) compared to 95° C. for activated carbon. Another importantresult was the beads absorbed only very small amount of mercury comparedto the activated carbon (FIG. 2). The selectivity of gold vs. copper(α_(Au,Cu)) was found to be nearly 40, while the α values for goldversus other contaminating metals were even higher.

The beads prepared as described above, and activated carbon were runthrough a second cycle with the synthetic flot-con solution. The beadsaccording to the present disclosure retained their performancecharacteristics, while activity of a comparative activated carbonabsorbent fell off dramatically. The beads also appeared to maintaintheir volume through the various loading, elution, and regenerationcycles.

The beads prepared as described above were run through 16 simulatedcycles for gold recovery from a pregnant solution. The cyclesrepresented gold loading, gold stripping, and regeneration of the beadsfor their next use. The cycles required large changes in pH (from 10.5to 1.5) and ionic strength, from mM (millimolar) to 2M (molar)solutions. The beads were shown to retain their gold capacity over the16 cycles, which for this formulation was found to be an extraordinary30 g Au/kg of MIP beads.

Absorption of Mercury

Macroreticular beads prepared as described above, except using phthalateas the surrogate molecule have a working capacity of about 16 g Hg/Kgbeads.

Mechanical Stability of the Beads

The beads prepared as described above were shown to be mechanically morerobust than activated carbon by a rather simple method. Three vials wereequipped with a stir bar and 10 mL of DI water with the pH adjusted to10.5. Into the first was placed 100 mg Amberlite 400, into the secondvial was placed 100 mg of the present beads, and into the 3^(rd) wasplaced 100 mg of activated carbon. All three vials were placed on stirplate and were stirred for 12 hours at 100 rpm. When finished, both theAmberlite resin and the beads were intact, while the activated carbonhad noticeably degraded with the solution above the activated carbonnearly opaque from the suspended carbon particles.

The invention can be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The foregoingembodiments are therefore to be considered in all respects illustrativerather than limiting on the inventions described herein. Scope of theinventions is thus indicated by the appended claims rather than by theforegoing description, and all changes that come within the meaning andrange of equivalency of the claims are intended to be embraced therein.

What is claimed is:
 1. A plurality of macroreticular polymer beadscomprising a copolymer having a plurality of complexing cavities whichselectively bind a target metal ion, wherein the copolymer is preparedfrom: (a) a ligand monomer which is cationic or anionic and is complexedto a non-metal surrogate ion, (b) a non-ligand monomer, and (c) acrosslinking monomer; wherein: (i) the charge of the copolymer in thecomplexing cavity is opposite the charge of the target metal ion, and(ii) the non-metal surrogate ion has substantially the same shape andcharge as the target metal ion.
 2. The macroreticular polymer beads ofclaim 1, wherein the ligand monomer is a cation.
 3. The macroreticularpolymer beads of claim 2, wherein the target metal ion is an anionicmetal complex.
 4. The macroreticular polymer beads of claim 3, whereinthe non-metal surrogate ion is an organic anion.
 5. The macroreticularpolymer beads of claim 3, wherein the non-metal surrogate ion is aninorganic anion.
 6. The macroreticular polymer beads of claim 1, whereinthe target metal ion is selected from the group consisting of Au(CN)₂ ⁻,Ag(CN)₂ ⁻, AuCl₄ ⁻, Au(S₂O₃)₂ ³⁻, Hg(CN)₄ ²⁻, and combinations thereof.7. The macroreticular polymer beads of claim 6, wherein when the targetmetal ion is Au(CN)₂ ⁻ or Ag(CN)₂ ⁻ the non-metal surrogate ion isthiocyanate, when the target metal ion is Au(S₂O₃)₂ ³⁻ the non-metalsurrogate ion is pentathionate, and when the target metal ion is Hg(CN)₄²⁻ the non-metal surrogate ion is isophthalate.
 8. The macroreticularpolymer beads of claim 1, wherein the beads have a selectivitycoefficient for the target metal ion greater than about
 10. 9. Themacroreticular polymer beads of claim 1, having a surface area of about0.1-500 m/g.
 10. The macroreticular polymer beads of claim 1, having anaverage particle size ranging from about 250 μm to about 1.5 mm.
 11. Themacroreticular polymer beads of claim 2, wherein the ligand monomer is apolymerizable cation selected from the group consisting of ammonium,pyridinium, pyrollidinium, imidizolium, guanidinium, phosphonium andsulfonium.
 12. The macroreticular polymer beads of claim 11, wherein theligand monomer is a 4-vinylbenzyl ammonium compound.
 13. Themacroreticular polymer beads of claim 12, wherein the ligand monomer isN,N,N-tripentyl-N-(4-vinylbenzyl) ammonium orN,N-dimethyl-N-decyl-N-(4-vinylbenzyl) ammonium.
 14. The macroreticularpolymer beads of claim 12, wherein the ligand monomer isN,N,N-tripentyl-N-(4-vinylbenzyl) ammonium.
 15. The macroreticularpolymer beads of claim 12, wherein the ligand monomer isN,N-dimethyl-N-decyl-N-(4-vinylbenzyl) ammonium.
 16. A method ofpreparing macroreticular molecularly imprinted polymer beads comprisingpolymerizing: (a) a ligand monomer which is cationic or anionic and iscomplexed to a non-metal surrogate ion, (b) an uncharged monomer, and(c) a crosslinking monomer; thereby forming a plurality ofmacroreticular molecularly imprinted polymer beads, each having aplurality of complexing cavities which selectively bind a target metalion, wherein the size and charge of the non-metal surrogate ion issubstantially the same as the target metal ion.
 17. The method of claim16, wherein the ligand monomer is a cation.
 18. The method of claim 17,wherein the target metal ion is an anionic metal complex.
 19. The methodof claim 18, wherein the non-metal surrogate ion is an organic anion.20. The method of claim 18, wherein the non-metal surrogate ion is aninorganic anion.
 21. The method of claim 18, wherein the target metalion is selected from the group consisting of Au(CN)₂ ⁻, Ag(CN)₂ ⁻, AuCl₄⁻, Au(S₂O₃)₂ ³⁻, Hg(CN)₄ ²⁻, and combinations thereof.
 22. The method ofclaim 21, wherein when the target metal ion is Au(CN)₂ ⁻ or Ag(CN)₂ ⁻the non-metal surrogate ion is thiocyanate, when the target metal ion isAu(S₂O₃)₂ ³⁻ the non-metal surrogate ion is pentathionate, and when thetarget metal ion is Hg(CN)₄ ²⁻ the non-metal surrogate ion isisophthalate.
 23. The method of claim 16, wherein the beads have aselectivity coefficient for the target ion of greater than about
 10. 24.The method of claim 16, wherein the macroreticular molecularly imprintedpolymer beads have a surface area of about 0.1-500 m²/g.
 25. The methodof claim 17, wherein the ligand monomer is a polymerizable cationselected from the group consisting of ammonium, pyridinium,pyrollidinium, imidizolium, guanidinium, phosphonium and sulfonium. 26.The method of claim 25, wherein the ligand monomer is selected from thegroup consisting of N,N,N-tripentyl-N-(4-vinylbenzyl) ammonium,N,N-dimethyl-N-decyl-N-(4-vinylbenzyl) ammonium,N,N,N-tripentyl-N-(4-vinylbenzyl) ammonium, andN,N-dimethyl-N-decyl-N-(4-vinylbenzyl) ammonium.
 27. A method ofselectively sequestering one or more target metal ions from a solutionof the one or more target metal ion ions admixed with other ions,comprising first contacting the macroreticular polymer beads of claim 1with a stripping solution, whereby the non-metal surrogate ions areremoved from the macroreticular polymer beads, then contacting thestripped beads with the solution, thereby selectively sequestering thetarget ion in the macroreticular polymer beads.
 28. The method of claim27, wherein the target ion is selected from the group consisting ofAu(CN)₂ ⁻, Ag(CN)₂ ⁻, Au(S₂O₃)₂ ³⁻, Hg(CN)₄ ²⁻, and combinationsthereof.
 29. A method of recovering gold from gold-containing ore,comprising: (1) crushing the gold-containing ore, (2) contacting thecrushed ore with a lixiviant, thereby forming an aqueous solutioncomprising an anionic gold complex, (3) contacting the aqueous solutionwith macroreticular polymer beads of claim 1, whereby the anionic goldcomplex is selectively complexed in the complexing cavities of thebeads, (4) stripping the beads with a stripping solution, whereby theanionic gold complex is substantially removed from the beads, (5)electrolytically reducing the recovered gold complex to form gold metal.30. The method of claim 29, wherein the lixiviant is aqueous chloride,the anionic gold complex is AuCl₄ ⁻, and further comprising, after step(2): (a) reducing the AuCl₄ ⁻ with a reducing agent to form Au⁺, (b)complexing the Au⁺ with aqueous cyanide to form an aqueous solution ofAuCN₂ ⁻, wherein in step (3), the aqueous solution of AuCN₂ ⁻ isselectively complexed in the complexing cavities of the beads.